1. Field of the Invention
The present invention relates to an apparatus for measuring an optical characteristic of an examined lens, which is utilized for estimating an optical characteristic of a lens such as a progressive focus lens and the like.
2. Description of Related Art
In conventional art, there is known a lens meter which projects a light flux for measurement to an examined lens, then detects a locus of a penetration of light by using a photo-detector, thereby enabling to measure an optical characteristic of the lens on the basis of detected results. The measurement is performed by way of locating a measuring point of a lens on a measuring optical axis, then obtaining a back vertex power thereof
However, in case of obtaining a distribution of each back vertex power at each point of an examined lens of which a power changes on a simple lens, such as a progressive focus lens and the like, the above mentioned apparatus causes trouble to measure. That is, the measurement should be performed repeatedly corresponding to a number of numerous measuring points, further, the measured numerous data should be recorded and analyzed with making them correspond to respective measuring points. Accordingly, it results in such disadvantages that it takes much time to perform measurement, and that measurement and analysis of data are remarkably trouble. Further, it is difficult for recording each measuring point corresponding to each measured result, thus tending to be inaccurate.
On the other hand, there is known an apparatus acting on so-called a moire topography. The apparatus projects a light on an examined lens, thereby causing moire fringes to be formed thereon, then analyzing the moire fringes, thereby obtaining a distribution of a principle point refractive power at each measuring point of the examined lens. However, the common moire topography does not allow the apparatus to obtain a distribution of a back vertex power which is defined as a refractive power of a spectacle lens, because the moire topography allows the apparatus to obtain a distribution of a principle point refractive power at each measuring point. In case of obtaining a distribution of each back vertex power at each measuring point by using an apparatus acting on an above mentioned moire topography, for which it is necessary to obtain a central thickness of the examined lens and a curvature of a minus surface. If measurement is performed in order to obtain these data prior to measure with acting on the moire topography, then a distribution of each back vertex power at each measuring point can be obtained. However, if the measuring mechanism therefor is additionally provided for the apparatus, then the apparatus may be large-sized, thus resulting in that it takes much time to perform measurement.
Further, the conventional measuring apparatus acting on the moire topography can not measure an amount of prism of the examined lens, therefore, it is not capable of judging an optical center of the examined lens.